Spatially resolved temperature measurement and irradiance control

ABSTRACT

A method, apparatus and system for producing a desired spatial temperature distribution across a workpiece. The method includes irradiating a plurality of areas on a surface of the workpiece to create localized heating of the workpiece in those areas, to produce the desired spatial temperature distribution in the workpiece, and the apparatus includes means for carrying out the method. The system includes a locator for locating the workpiece in a desired position relative to an energy source, and an irradiance system for carrying out the method. The system further includes a processor circuit in communication with the irradiance system, and a radiation-absorbing environment. The irradiance system includes a measuring system and at least one energy source for directing radiation to the surface of the workpiece.

FIELD OF THE INVENTION

This invention relates to irradiance of a workpiece, and moreparticularly to producing a desired spatial temperature distributionacross a workpiece.

BACKGROUND OF THE INVENTION

The manufacture of a semiconductor involves a number of thermal cycles,in which a wafer, typically silicon, is heated from room temperature toa high temperature such as 900° C., for example. Significantly higher orlower temperatures may be required depending upon the particularapplication. The wafer is heated relatively quickly, with a typical ramprate of at least 100° C. per second.

During such heating cycles, it is critically important that all pointson the wafer remain at a uniform temperature relative to one another. Ifthe temperature distribution across the wafer is non-uniform, thermalgradients will cause the crystal planes within the wafer to slip,thereby breaking the crystal lattice. A very small spatial movement, onthe order of 0.2 μm, may completely destroy the crystal lattice. Thermalgradients may also cause other damage, such as warpage or defectgeneration. Even in the absence of slippage, a non-uniform temperaturedistribution across the wafer may cause non-uniform performance-relatedcharacteristics, resulting in either inadequate performance of theparticular wafer, or undesirable performance differences from wafer towafer.

Thus, the industry defines a “process window”, which is an acceptabletemperature range in which the temperature of each portion of the wafermust be kept in order to maintain performance goals. In the past, anon-uniformity of no more than ±10° C. across the wafer at all timesduring the thermal cycle was acceptable.

However, with the manufacture of increasingly high performancesemiconductor computer chips, and as larger numbers of device featuresare required on increasingly compact chips, an increasingly uniformtemperature distribution across the wafer is required at all timesthroughout the thermal cycles, i.e. both during ramp and at a processtemperature, which is usually a constant temperature. Industry roadmapsindicate that for devices with 0.25 μm spacing, at a process temperatureof 1100° C. a temperature uniformity of ±3° C. (i.e. 3° C.=3σ where σ isthe standard deviation of the temperature distribution across the wafer)will be required, and temperature uniformity of ±1° C. (3σ) will berequired for devices with 0.18 μm spacing.

In addition, faster ramp rates, on the order of 400° C. per second orhigher, will be desired in the near future.

Conventional rapid thermal processing (RTP) techniques do not appear tobe capable of achieving either the required degree of uniformity or thedesired ramp rate.

One example of a conventional RTP technique includes rotating a wafer,and heating the wafer with a large number of tungsten-halogen lamps,each of which channels radiation toward the wafer surface through one ofa large number of light pipes. Wafer temperature is measured with acomparatively small number of stationary pyrometers, each of whichmeasures radiation thermally emitted by the wafer. Each measuringpyrometer is located at a different radial distance from the centre ofthe rotating wafer, so that the resulting temperature profile describesthe average temperatures around a number of annular rings of the wafer,each annular ring corresponding to the radial distance of a particularmeasuring pyrometer. The resulting temperature versus time profile isthen entered into a control computer, which employs a number of feedbackcontrol loops to control the power to the individual lamps or group oflamps associated with each pyrometer or sensor.

This technique has a disadvantage, in that it lacks the ability todetect or correct for temperature differences between any two pointslying in the same annular ring, due to the constant rotation of thewafer relative to the pyrometers. Thus, while this technique is able tomaintain a number of annular rings at relatively uniform averagetemperatures, it is not capable of either detecting or correcting forcircumferential temperature differences. A mere 1% variation ofabsorption from one side of the wafer to the other may cause more than a3° C. temperature variation at 1050° C. Thus, this technique is notsuitable for the current industry requirements.

Also, to ensure accurate measurements, the plurality of pyrometers mustbe carefully calibrated, resulting in additional time and effort.

Modifying this technique for a non-rotating wafer would require a largeincrease in the number of pyrometers, which would lead to seriouscalibration difficulties, in addition to the added expense anddifficulty of designing the hardware and software required toaccommodate a large plurality of pyrometers and related control loops.

A further difficulty arises from reflection, by the walls of the processchamber, of radiation reflected or thermally emitted by the wafer. Suchreflections may heat the wafer in a non-uniform manner, and may alsoproduce measurement errors.

The substitution of a camera or CCD in this technique would not bepractical, partly because the process hardware tends to obscure the viewof the wafer, and partly because a camera or CCD would be particularlysusceptible to errors induced by internally reflected radiation.

Furthermore, the use of a plurality of heat sources requires manualcalibration of each such heat source, with the result that simplereplacement of a burnt-out bulb may become a tedious and time-consumingprocess.

Moreover, the spectral distribution of tungsten-halogen heat sources maypose additional undesirable effects. Tungsten irradiance sourcestypically produce only 40% of their spectral energy below the 1.2 μmband gap absorption of room-temperature silicon, resulting in aninefficient thermal cycle. Also, the wavelengths generated by tungstensources may be sufficiently long to penetrate through a substrate sideof the wafer and be non-uniformly absorbed by highly-doped features on adevice side of the wafer, resulting in an increasingly non-uniformtemperature distribution. Such an effect may be aggravated in devicesinvolving insulating layers such as silicon on oxide (SOI). Irradiancefields produced by tungsten sources may be red-shifted as the powersupplied to the source is decreased, resulting in even greaterinefficiency and greater penetration of radiation into the device side.

In addition, as the temperature of silicon increases, it is able toabsorb increasingly longer wavelengths of radiation. Thus, hotter areasof the wafer may absorb greater amounts of energy at the longerwavelengths produced by tungsten-halogen sources than cooler areas ofthe wafer, resulting in faster heating of the hotter areas and thermalrunaway.

An additional problem arises from the slow thermal time constants oftungsten lamps. Fast ramp rates to desired process temperatures requirefast feedback controls. For example, heating at 500° C./sec to a processtemperature with a uniformity of ±1° C. ideally requires a response timeof ±2 ms (±1° C./500° C./sec), whereas tungsten lamps typically havemuch longer response times of fractions of a second.

Finally, this technique does not appear to be capable of achieving aramp rate of 400° C. per second which will soon be desired.

Thus, there is a need for a better heating device for semiconductorprocessing.

SUMMARY OF THE INVENTION

Specific embodiments of the current invention address the above need bydynamically producing a high-resolution spatially resolved temperatureprofile of the temperature distribution across an entire surface of aworkpiece throughout a thermal cycle, and using this spatially resolvedtemperature profile to produce and maintain a desired temperaturedistribution at all points across the surface, at all times during thethermal cycle.

In accordance with one aspect of the invention, there is provided amethod and an apparatus for producing a desired spatial temperaturedistribution across a workpiece. The method includes irradiating aplurality of areas on a surface of the workpiece to create localizedheating of the workpiece in the areas, to produce the desired spatialtemperature distribution in the workpiece. Preferably, irradiatingincludes exposing each one of the plurality of areas to radiation toproduce the localized heating. The method may further include producinga representation of an instantaneous spatial temperature distribution inthe workpiece, and producing an instantaneous spatial temperature errordistribution as a function of the desired spatial temperaturedistribution and the instantaneous spatial temperature distribution.Preferably, the method includes absorbing radiation exitant from thesurface. Producing the representation may include producing at least onesignal representative of radiation intensity from the surface. Themethod may further include controlling the amount of the localizedheating by irradiating in response to the instantaneous spatialtemperature error distribution. Optionally, exposing includes directingradiation from at least one energy source to the surface, andselectively varying, as a function of the representation, a variableopacity of each of a plurality of filter portions of a filtering memberinterposed between the at least one energy source and the surface. Theapparatus includes means for carrying out the method.

In accordance with another aspect of the invention, there is provided asystem for producing a desired spatial temperature distribution across aworkpiece. The system includes a locator for locating the workpiece in adesired position relative to an energy source, and an irradiance systemfor irradiating a plurality of areas on a surface of the workpiece tocreate localized heating of the workpiece in the areas, to produce thedesired spatial temperature distribution in the workpiece. Preferably,the system includes a processor circuit in communication with theirradiance system, and the processor circuit is programmed to controlthe irradiance system to expose each one of the plurality of areas toradiation to produce the localized heating. The irradiance system mayinclude a measuring system for producing a representation of aninstantaneous spatial temperature distribution in the workpiece.

Optionally, the processor circuit is programmed to control the measuringsystem to produce an instantaneous spatial temperature errordistribution as a function of the desired spatial temperaturedistribution and the instantaneous spatial temperature distribution.Preferably, the system further includes a radiation absorbingenvironment for absorbing radiation exitant from the surface.

The measuring system preferably includes an imaging system. The imagingsystem may include a charge-coupled device, and the processor circuitmay be programmed to control the charge-coupled device to produce atleast one signal representative of the surface.

Preferably, the irradiance system includes at least one energy source,which may be an arc lamp, for directing radiation to the surface. Theirradiance system may further include a filtering member interposedbetween the at least one energy source and the surface, the filteringmember having a plurality of filter portions, each of the plurality offilter portions having a variable opacity, and the processor circuit isprogrammed to selectively vary, as a function of the representation, thevariable opacity of each of the plurality of filter portions, therebyproducing the desired spatial temperature distribution in the workpiece.

When applied to a semiconductor wafer as a workpiece, the measurementsystem has a spatial resolution finer than the preferred smallestthermal scale length in the system and a time response faster than theshortest system time constant. Preferred embodiment of the inventionemploy a minimal number of measurement devices and a minimal number ofheat sources, thus avoiding calibration difficulties and added expenses.Such embodiments also minimize the effects of reflection by the chamberwalls of radiation emitted or reflected by the wafer, thereby minimizingan additional source of non-uniform heating of the wafer and alsominimizing a source of measurement error which would otherwise interferewith the ability to produce the desired temperature distribution. Ashort-wavelength arc lamp may be employed as a primary irradiancesource, resulting in highly efficient absorption in a thin surface ofthe substrate side of the wafer, with virtually no penetration of theradiation into the device side. Finally, embodiments of the currentinvention capable of producing ramp rates on the order of 400° C. persecond or even higher may be constructed. Thermal time constants of lessthan 1 ms for arc lamps make control of these fast ramps possible.

In addition to producing a uniform temperature distribution throughout athermal cycle, embodiment of the invention may just as easily be used toproduce any particular desired non-uniform temperature distribution, orto produce a dynamically changing series of desired temperaturedistributions.

Further aspects of the present invention will be apparent to one ofordinary skill in the art upon reviewing the specific embodimentsdescribed in the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate various embodiments of the invention,

FIG. 1 is a fragmented perspective view of a system for producing adesired spatial temperature distribution across a workpiece, accordingto a first embodiment of the invention;

FIG. 2 is a cross-sectional view of a corrective energy source of thesystem shown in FIG. 1;

FIG. 3 is a sectional view of the corrective energy source shown of FIG.1, on line 3—3 shown in FIG. 2;

FIG. 4 is a fragmented schematic representation of the workpiece, ameasuring device and the corrective energy source of the system of FIG.1;

FIG. 5 is a block diagram of memory and a storage device accessible by aprocessor circuit of the system of FIG. 1;

FIG. 6 is a block diagram of a control routine executed by the processorcircuit;

FIGS. 7A-7C are graphical representations of a hypothetical temperaturecurve of a cross-section of the workpiece shown in FIG. 1;

FIG. 8 is a fragmented perspective view of a system for producing adesired spatial temperature distribution across a workpiece, accordingto a second embodiment of the invention;

FIG. 9 is a cross-sectional view of a corrective energy source of asystem for producing a desired spatial temperature distribution across aworkpiece, according to a third embodiment of the invention;

FIG. 10 is a cross-sectional view of a corrective energy source of asystem for producing a desired spatial temperature distribution across aworkpiece, according to a fourth embodiment of the invention;

FIG. 11 is a cross-sectional view of a corrective energy source of asystem for producing a desired spatial temperature distribution across aworkpiece, according to a fifth embodiment of the invention;

FIG. 12 is a fragmented perspective view of a system for producing adesired spatial temperature distribution across a workpiece, accordingto a sixth embodiment of the invention;

FIG. 13 is a cross-sectional view of a corrective energy source of thesystem shown in FIG. 12;

FIG. 14 is a perspective view of a corrective energy source of a systemfor producing a desired spatial temperature distribution across aworkpiece, according to a seventh embodiment of the invention;

FIG. 15 is a cross-sectional view of a measuring device of a system forproducing a desired spatial temperature distribution across a workpiece,according to an eighth embodiment of the invention;

FIG. 16 is a cross-sectional view of a measuring device of a system forproducing a desired spatial temperature distribution across a workpiece,according to a ninth embodiment of the invention; and

FIG. 17 is a cross-sectional view of a measuring device of a system forproducing a desired spatial temperature distribution across a workpiece,according to a tenth embodiment of the invention.

DETAILED DESCRIPTION

The present embodiment of the invention dynamically produces ahigh-resolution spatially resolved temperature distribution profile ofan entire surface of a workpiece throughout a thermal cycle, and usesthis spatially resolved temperature distribution profile to produce andmaintain a desired temperature distribution at all points across thesurface, at all times during the thermal cycle.

As shown in FIG. 1, a system for producing a desired spatial temperaturedistribution across a workpiece is designated generally by the referencecharacter 20. The system includes a chamber 22 having an upper and alower portion 24 and 26 respectively, separated by a horizontal internalwall 28. The internal wall 28 has a circular opening 30 in which a guardring 32 for holding a workpiece 34 is set.

In this embodiment, the workpiece 34 is a silicon wafer used to producesemiconductor chips. The workpiece 34 has an upper surface 33, which isgenerally a device side, and a lower surface 35, which is generally asubstrate side.

The upper portion 24 of the chamber 22 is defined by the internal wall28, by a first upper portion 37 of a first side wall 36 and a secondupper portion 45 of a second side wall 44 which rise above the internalwall 28, by similar upper portions of two side walls not shown, and by aceiling (not shown) parallel to and above the internal wall 28, attachedto a first top surface 39 and a second top surface 47 of the side walls36 and 44 respectively and to similar top surfaces of the two side wallsnot shown.

The lower portion 26 of the chamber 22 is enclosed by the internal wall28, the guard ring 32 and the workpiece 34, by the first and second sidewalls 36 and 44 and two further side walls (not shown), by first, secondand third lower angled walls 38, 40 and 42, and by first and secondangled windows 48 and 50. The walls 36, 38, 40, 42, 44 and a lowersurface 46 of the internal wall 28 include radiation-absorbing material,which in this embodiment is black stainless steel. The lower portion 26of the chamber 22 is thus a “black chamber” or radiation-absorbingenvironment.

A radiation sensor 49 is housed within the internal wall 28, laterallydisposed between the guard ring 32 and the first side wall 36, coplanarto the workpiece 34. The second angled window 50 extends downwardly andinwardly from the second side wall 44 somewhat below the horizontalinternal wall 28 to the bottom of the third lower angled wall 42 at abase of the chamber 22, and is interposed between the workpiece 34 and aprimary energy source 52.

In this embodiment, the primary energy source 52 includes an arc lamp 54disposed approximately 30 cm beneath the lower surface 35 of theworkpiece.

The primary energy source 52 further includes a reflector system 56extending around and beneath the arc lamp 54 to focus radiation towardthe workpiece 34.

The first angled window 48 is sealed within an opening 58 formed in theplane of the first lower angled wall 38. A corrective energy sourceshown generally at 60 and a measuring device 62 are disposed beneath thefirst angled window 48 (distally from the workpiece 34 ).

The primary energy source 52, the corrective energy source 60, themeasuring device 62 and the radiation sensor 49 are connected via cables63, 64, 65 and 67 respectively for communication with a processorcircuit 66, which in this embodiment is housed within a general purposecomputer 68 having an input device 69 and a display 70. Effectively, theprimary energy source 52 and the corrective energy source act togetheras means for irradiating, the primary energy source acting as primarymeans for irradiating and the corrective energy source acting ascorrective means for irradiating.

Generally, the processor circuit 66 controls the primary energy source52 and/or the corrective energy source 60 to produce a radiation imageon the workpiece in response to a thermal image at the workpiece, asmeasured by the measuring device 62.

More particularly, the measuring device 62 periodically measures datarepresenting a spatial temperature distribution across the lower surface35 of the workpiece 34. If the processor circuit 66 detects anydeviations from a desired temperature distribution, the processorcircuit will cause the corrective energy source to selectively irradiateparticular areas of the lower surface to correct such deviations. Forexample, if the desired temperature profile is a uniform temperaturedistribution, and the processor circuit detects a “hot spot”, theprocessor circuit will cause the corrective energy source to applyproportionally greater radiation to all other areas of the workpiece 34than the hot spot, thus heating the cooler areas to arrive at thedesired uniform temperature distribution.

Chamber

To achieve suitable accuracy in temperature measurement, it is desirablethat the lower portion 26 of the chamber 22 act as a “black chamber”. Toachieve this, the internal wall 28, the first and second side walls 36and 44 and the two other side walls not shown, and the three lowerangled walls 38, 40 and 42, are made of black stainless steel.

Alternatively, other suitable radiation-absorbing materials could beused, such as anodized aluminum for example. Or, the walls could becomposed of virtually any thermally conductive material and coated witha radiation-absorbing substance such as black nickel coating or paintcontaining graphite, for example.

The radiation-absorbing surfaces may be covered with (or alternatively,made from) non-contaminating material, such as SiO₂ (quartz), forexample. Thus, the inside surfaces of the chamber 22 may be formed ofnon-contaminating material such as quartz, with back surfaces formed ofradiation-absorbing material.

When radiation from the primary energy source 52, the corrective energysource 60, or radiation exitant from the lower surface 35 of theworkpiece 34 strikes any of the walls forming the lower portion 26 ofthe chamber, such radiation is absorbed rather than reflected. Thus,each of the above walls acts as a radiation-absorbing surface forabsorbing radiation exitant from the workpiece surface.

In this specification, including the claims, the noun “exitance” andcorresponding adjective “exitant”, in relation to radiation from asurface, mean radiant exitance, i.e., the total power at all wavelengthsleaving a unit area surface. “Radiation exitant” from the lower surface35 of the workpiece 34 thus includes radiation both reflected andthermally emitted by the lower surface at all wavelengths.

Additionally, the walls 28, 36, 38, 40, 42 and 44 and the two side walls(not shown) are water-cooled by a cooling system 29 for cooling theradiation absorbing surfaces, to prevent the temperature of the wallsfrom increasing as radiation is absorbed, thus inhibiting thermalemission of radiation by the walls. The water-cooled,radiation-absorbing walls 28, 36, 38, 40, 42 and 44 thus act as aradiation-absorbing environment which includes at least one radiationabsorbing surface.

The second and third lower angled walls 40 and 42 rise upwardly from thebase of the chamber 22 and inwardly toward the centre of the chamber,and intersect to form an inverted-“V”-shaped barrier 72 interposedbetween the second angled window 50 and the first lower angled wall 38.The barrier 72 rises to a sufficient height within the lower portion 26of the chamber 22 to completely block the second angled window 50 fromthe view of the first angled window 48, preventing radiation fromtravelling directly from the primary energy source 52 or the secondangled window 50 to the measuring device 62.

Similarly, the first lower angled wall 38 in which the first angledwindow 48 is mounted extends upwardly and outwardly from the bottom ofthe second lower angled wall 40 at the base of the chamber to intersecta side wall (not shown). The second angled window 50 and the first lowerangled wall 38 in which the first angled window 48 is mounted are thusoriented so as to rise vertically and outwardly from the base of thechamber 22, at angles sufficiently steep to ensure that the windows donot reflect radiation emitted or reflected by the workpiece 34 back tothe workpiece.

Thus, since the walls 28, 36, 40 and 44 are radiation-absorbing, theonly source of radiation within the field of view of the measuringdevice 62 is the workpiece 34. The composition and configuration of thewalls 28, 36, 38, 40, 42, and 44 and the first and second angled windows48 and 50 thus prevent reflection from system components frominterfering with measurements taken by the measuring device 62 therebyimproving the accuracy of temperature measurements, and also minimizenon-uniform heating of the workpiece 34 resulting from internalreflection.

In this embodiment, the first and second angled windows 48 and 50 arecomposed of quartz. It will be appreciated that quartz may absorbinfrared radiation thermally emitted by the workpiece, and begin tothermally emit radiation as its temperature rises. To minimize suchabsorption and thermal emission, the first and second angled windows 48and 50 are water-cooled by the cooling system 29.

Additionally, the reflective surfaces of the reflector system 56 areoriented so as to minimize any reflection back to the workpiece ofradiation exitant from the workpiece.

Near the top of the chamber 22, the guard ring 32 includes the same orsimilar material as the workpiece, which in this embodiment is silicon.The guard ring is used to reduce edge effects during the thermal cycle,and acts as a locator for locating the workpiece in a desired positionrelative to an energy source.

In this embodiment, each of the surfaces of the upper portion 24 of thechamber 22—i.e., an upper surface of the internal wall 28, the first andsecond upper portions 37 and 45 of the first and second side walls 36and 44 and the similar upper portions of the two side walls not shown,and the ceiling (not shown)—are coated with a highly reflective coating.Thus, in this embodiment the upper portion 24 of the chamber 22 is areflecting chamber.

Alternatively, however, the surfaces of the upper portion 24 of thechamber 22 may be radiation-absorbing and water-cooled, as describedabove in the context of the lower chamber, such that the upper portionforms a second “black chamber” or radiation-absorbing environment.

Or, as a further alternative, specific area segments of the surfaces ofthe upper portion may be reflective, with the remainder of the surfacesbeing radiation-absorbing. The reflective segments may either have auniform reflectivity, or alternatively may have differentreflectivities. Such reflective segments may be used to improveuniformity.

Primary Energy Source

In this embodiment, the primary energy source 52 includes a water wallarc lamp 54 manufactured by Vortek Industries Ltd. of Vancouver, Canada.In the present embodiment, a 300 kW arc lamp is used, although customarc lamps with powers up to the order of 1.5 MW could be substituted.The ability to produce hundreds of kilowatts of radiation with a singlesource enhances uniformity, eliminates the need for calibration of alarge number of energy sources, such as an array of tungsten lamps, forexample, and similarly eliminates the need for frequent replacement andre-calibration of burned-out bulbs.

In this embodiment, the spectral distribution of the irradiance producedby the arc lamp 54 ranges from 0.2 μm to 1.4 μm, resulting in highlyefficient absorption by the workpiece, since over 95% of the arc'sradiation is below the 1.2 μm band gap absorption of cold silicon,compared with only 40% for a typical tungsten source, for example.

In addition to increasing absorption efficiency, the shorter wavelengthof the arc lamp radiation ensures that such radiation will be absorbedin a relatively thin layer of the lower surface 35 of the workpiece 34.Consequently, the device side or upper surface 33 of the workpiece willbe heated only by conduction through the wafer. In contrast, radiationof longer wavelengths such as those produced by tungsten would penetratefurther into the wafer, and may be non-uniformly absorbed byhighly-doped features on the device side, resulting in an additionalsource of non-uniform heating.

The spectral distribution of the radiation emitted by the arc lamp 54 isalso constant with power, in contrast with tungsten sources which arered-shifted as power is reduced resulting in even lower absorptionefficiency and increased penetration into the workpiece.

The processor circuit 66 produces primary energy source control signalsto control the arc lamp 54 on and off and to continuously vary theintensity of radiation emitted by the arc lamp. The arc lamp 54 has afast response time, on the order of one microsecond. Effectively,therefore, the response time of the arc lamp 54 is limited only by theresponse time of its power supply, which may be as fast as tenmicroseconds, for example. In this embodiment, therefore, the irradiancesystem includes at least one arc lamp, which has a response time of lessthan one millisecond. The response time of the arc lamp is thussignificantly shorter than the time constant of thermal properties of asilicon wafer. This makes it ideally-suited to emissivity-compensatedtemperature measurements (discussed below). The fast response time ofthe arc lamp also permits accurate feedback control during fasttemperature ramps.

The reflector system 56 is shaped so as to cooperate with the arc lamp54 to produce a generally uniform irradiance field across the lowersurface 35 of the workpiece and the radiation sensor 49. However, itwill be appreciated that uniform primary irradiation incident on theworkpiece does not necessarily produce uniform temperatures across thelower surf ace. For this reason, the corrective energy source is used.

Corrective Energy Source

Referring to FIG. 1, in the present embodiment the corrective energysource 60 is an LCD projector device. The corrective energy source 60has a body 74 and a first focal barrel 76. A front opening 77 of thefirst focal barrel 76 is located directly beneath the first angledwindow 48. Located within the body 74 of the corrective energy source 60are a secondary energy source 78, a reflector 80, and an LCD panel 82interposed between the secondary energy source and the first focalbarrel. The corrective energy source is oriented so that a central axis83 of the first focal barrel 76 passes directly through a centre 85 ofthe workpiece 34 and through the centre of the LCD panel 82. The LCDpanel is mounted normal to the central axis 83 of the first focal barrel76 so that energy from the secondary energy source passes directlythrough the LCD panel 82 through the first focal barrel to the lowersurface 35 of the workpiece.

Referring to FIG. 2, the corrective energy source 60 is shown in greaterdetail. The reflector 80 is located at a rear portion 75 of the body 74,while the LCD panel 82 is located at a front portion 79 of the body,immediately behind a rear opening 81 of the first focal barrel 76. Thesecondary energy source 78, which in this embodiment is an arc lamp, isinterposed between the ref lector 80 and the LCD panel 82.

An LCD imaging optics system 84, illustrated by a representative lens inFIG. 2, is housed within the first focal barrel 76. The LCD imagingoptics system 84 is somewhat similar to a conventional imaging opticssystem used for LCD projectors which connect to laptop computers,although a lower resolution will suffice for the purposes of the presentembodiment than required for laptop computer projection presentations.The reflector 80 is shaped so as to cooperate with the secondary energysource 78 and the LCD imaging optics system 84 to produce a generallyuniform irradiance field across the lower surface 35 of the workpiece,apart from the selective effects of the LCD panel 82. The correctiveenergy source thus acts as at least one energy source for directingradiation to the lower surface of the workpiece.

Referring to FIG. 3, the LCD panel 82 is shown in greater detail. TheLCD panel includes a plurality of elements or image producing “pixels”86. Preferably, the LCD panel comprises at least 32×32 image producingpixels; however, depending on the particular application, asignificantly lower density, such as 10×10 pixels for example, maysuffice. The light transmissivity of each image producing pixel of theLCD panel 82 is controllable in response to electrical image controlsignals produced by the processor circuit 66. In this embodiment, eachimage producing pixel has a greyscale of 16 shades of grey, so that anyindividual image producing pixel may be controlled to assume any one ofthe 16 discrete shades of grey, or degrees of light transmission.Alternatively, an LCD panel with image producing pixels having a largernumber of degrees of light transmission, such as 256 shades of grey forexample, may be substituted. Radiation from the secondary energy source78 arriving at a particular pixel will either be completely blocked bythe pixel, partly blocked, or pass through the pixel essentiallyundiminished (subject to minimum inherent power loss of an LCD panel),depending upon which of the 16 shades of grey has been assigned to thatpixel. For example, FIG. 3 illustrates a transparent pixel 88, a darkerpixel 90, an even darker pixel 92, and a totally opaque pixel 94

Referring back to FIG. 2, in effect, the LCD panel acts as a filteringmember or radiation image producing device interposed between thesecondary energy source 78 and the lower surface 35 of the workpiece,and the plurality of image producing pixels 86 of the LCD panel acts asa plurality of filter or image portions, each having a variable opacityto effectively discretely define a radiation image. Ref erring to FIGS.3 and 4, the LCD imaging optics system 84 projects the radiation image,defined by the LCD panel 82, onto the entire lower surface 35 of theworkpiece 34.

As shown in FIG. 4, light passing through a particular one of the imageproducing pixels 86 on the LCD panel 82 will be focused by the LCDimaging optics system 84 upon a particular corresponding one of aplurality of projection areas 96 on the lower surface 35 of theworkpiece 34. In this embodiment, each workpiece projection areacorresponding to a given image pixel is approximately 1 cm by 1 cm. Thedarker the shade of grey assigned by the processor circuit to aparticular image producing pixel on the LCD panel, the less energy willbe received at the projection area 96 of the lower surface 35 of theworkpiece corresponding to that pixel.

Measuring System

As shown in FIG. 1, the measuring device 62 includes a body 102 and asecond focal barrel 104. A front opening 106 of the second focal barrel104 is located directly beneath the first angled window 48. Themeasuring device 62 is oriented such that a central axis 105 of thesecond focal barrel 104 passes through the centre 85 of the workpiece34.

In this embodiment, the measuring device 62 includes a charge-coupleddevice (CCD) 98 capable of detecting relative temperature differences of±0.25° C., and a CCD camera optics system 108 illustrated by arepresentative lens in FIG. 1. The CCD 98 is centred about and normal tothe central axis 105 of the second focal barrel 104.

A band-pass filter 100 is disposed within the second focal barrel 104.In this embodiment, the filter is transparent to incident radiation fromthe workpiece having wavelengths of λ=900±5 nm, and is opaque to otherwavelengths. Thus, the measuring system includes a filter interposedbetween the workpiece and the charge-coupled device, the filter beingtransparent to radiation within a predetermined wavelength bandwidth andotherwise opaque. The predetermined wavelength bandwidth is centredabout 900 nm.

The CCD camera optics system 108 projects an image of the entire lowersurface 35 of the workpiece 34 onto the CCD 98. Referring to FIG. 4,radiation reflected or thermally emitted by each one of a plurality ofmeasurement areas 110 on the lower surface 35 of the workpiece 34 isfocused by the CCD camera optics system 108 onto a particularcorresponding one of a plurality of measurement pixels 112 on the CCD98. Effectively, the measuring device provides measurement signalsrepresenting a thermal image projected onto the CCD. Thus, the measuringsystem includes an imaging system, which in this embodiment is acharge-coupled device, and the processor circuit is programmed tocontrol the charge-coupled device to produce at least one signalrepresentative of the surface. Alternatively, however, other suitableimaging systems may be substituted.

In this embodiment, a 240×750 pixel CCD is used, so that each one of themeasurement pixels 112 on the CCD 98 corresponds to a measurement area110 of less than 1 mm² on the lower surface 35 of the workpiece. Asomewhat lower resolution would also suffice, provided the individualmeasurement areas 110 measured by the CCD are appreciably smaller thanthe individual projection areas 96 onto which radiation is selectivelyprojected by the corrective energy source 60, so that the measurementresolution is finer than the projection resolution of the correctiveenergy source.

In this embodiment, each image producing pixel effectively controlsradiation incident upon a projection area of the workpiece measuring10×10=100 measurement pixels.

The measuring system further includes the radiation sensor 49 housedwithin the internal wall 28, laterally disposed between the guard ring32 and the first side wall 36, coplanar to the workpiece 34. An opening(not shown) in the lower surface 46 of the internal wall 28 allowsradiation from the primary energy source 52 to be received at theradiation sensor 49. Since the primary energy source 52 produces agenerally uniform irradiance field in the vicinity of the lower surface35 of the workpiece 34, the intensity of incident radiation from theprimary energy source 52 received at the radiation sensor 49 is equal tothe intensity of incident radiation received at any measurement area 110on the lower surface 35 of the workpiece. Effectively, therefore, theradiation sensor produces sensor signals representing an intensity ofincident radiation received from the primary energy source 52 at thelower surface 35 of the workpiece 34.

In this embodiment, the radiation sensor 49 is a photo diode. However,any other type of radiation sensor with a suitably fast response timemay be substituted therefor.

Processor Circuit

Referring to FIGS. 1 and 5, in this embodiment the processor circuit 66housed within the general purpose computer 68 includes a microprocessor120. The microprocessor 120 is in communication with a peripheralinterface 126 for permitting the microprocessor 120 to receive signalsfrom the input device 69, to communicate control signals to and receivemeasurement signals from the measuring device 62, to communicate controlsignals to and receive sensor signals from the radiation sensor 49, andto communicate primary energy source control signals to the primaryenergy source 52, corrective energy source signals to the correctiveenergy source 60 and display control signals to the display 70. Themicroprocessor 120 is further connected to a random-access memory (RAM)130 and to a storage device 150, which in this embodiment includes ahard disk.

The storage device 150 stores instruction codes 152, which in thisembodiment are operable to direct the microprocessor 120 to execute arapid thermal processing (RTP) control routine 154.

The RTP control routine 154 directs the microprocessor 120 to define aplurality of storage areas in the RAM 130 including:

1) an incident intensity store 131 for storing a representation producedby the radiation sensor 49 of an intensity of radiation incident uponthe lower surface 35 of the workpiece;

2) a total radiation store 132 for storing a representation produced bythe measuring device 62 of an intensity of radiation both reflected andthermally emitted by the lower surface 35 of the workpiece;

3) a thermal radiation store 133 for storing a representation of areceived thermal image of the workpiece produced by the measuringdevice;

4) an emissivity store 134 for storing a representation of an emissivityimage of the lower surface of the workpiece;

5) a temperature store 136 for storing a calculated representation of anabsolute temperature image of the workpiece;

6) a temperature error store 138 for storing a calculated representationof deviations from a desired temperature distribution across theworkpiece;

7) a corrective power store 140 for storing a representation of acorrective power image;

8) a display store 142 for storing a representation of a display imageto be displayed on the display 70:

9) a timer store 146 for storing timer values;

10) a parameter store 156 for storing parameters defining a desiredthermal cycle; and

11) an instantaneous desired temperature distribution store 158 forstoring a representation of a desired temperature distribution acrossthe lower surface at a given instant during the thermal cycle.

Each of the total radiation, emissivity, thermal radiation, temperature,temperature error, display and desired temperature distribution stores132, 133, 134, 136, 138, 142 and 158 is configured to store atwo-dimensional array of values, each value representing a physicalproperty of a particular one of the plurality of measurement areas 110on the lower surface 35 of the workpiece 34. The incident intensitystore 131 is configured to store a single value representing theintensity at each of the measurement areas 110 on the lower surface 35of incident radiation produced by the primary energy source 52. Thecorrective power store 140 is configured to store a two-dimensionalarray of correction values, each value corresponding to a particularimage producing pixel 86 on the LCD panel 82 and thus to a correspondingparticular one of the plurality of projection areas 96 on the lowersurface 35 of the workpiece 34.

The RTP control routine 154 further directs the microprocessor 120 todefine in the storage device 150 a parameter folder 157 for storingparameters for one or more pre-defined thermal cycles, a desiredtemperature distribution folder 159 for storing a plurality ofrepresentations of desired temperature distributions across the lowersurface of the workpiece at respective instants in time during thethermal cycle at which the temperature of the workpiece is to bemeasured, and an archive folder 160 for storing information pertainingto the thermal cycle. It will be appreciated that the images in any ofthe memory stores, such as the representations of spatial temperaturedistribution across the workpiece stored in the temperature store 136for example, may be archived for subsequent retrieval and review, thusmaintaining a record of the thermal cycle.

Operation

The RTP control routine 154 directs the processor circuit 66 tocooperate with the primary energy source 52, the corrective energysource 60, the measuring device 62, the radiation sensor 49 and theinput device 69, in order to produce the desired thermal cycle. The RTPcontrol routine 154 governs both the macroscopic parameters such as howquickly the workpiece is to be heated and the maximum temperature of thethermal cycle, and the microscopic parameters by correcting deviationsfrom the desired temperature distribution across the workpiecethroughout the thermal cycle.

Essentially, in addition to directing the processor circuit 66 tocontrol the primary energy source 52 in accordance with the parametersdefining the desired thermal cycle, the RTP control routine 154 directsthe processor circuit to periodically measure a spatial temperaturedistribution across the lower surface 35 of the workpiece 34. Upondetecting deviations from the desired temperature distribution, theprocessor circuit controls the corrective energy source 60 toselectively deliver a greater amount of heat to projection areas on thelower surface which are too cool, the greater amount of heat varying indirect proportion to the temperature difference between each of thecooler areas and the projection area on the workpiece which is hottestrelative to its desired temperature.

However, particular measurement areas 110 of the lower surface 35 mayhave slightly different emissivities than other measurement areas 110,with the result that two of the measurement areas, even though at thesame temperature, might thermally emit different intensities ofradiation, and conversely, two areas at different temperatures mightthermally emit identical intensities of radiation due to their differentemissivities. Thus, in order to accurately measure the spatialtemperature distribution across the workpiece, the followingemissivity-corrected temperature measurement process is adopted.

First, the intensity of radiation reflected and thermally emitted byeach of the plurality of measurement areas 110 on the lower surface 35is measured. Next, the intensity of thermal radiation thermally emittedby each of the measurement areas 110 is measured. Reflectivity andemissivity of each measurement area are calculated from the twomeasurements. Finally, the temperature of each of the plurality ofmeasurement areas is calculated as a function of the thermal radiationand emissivity results.

Referring to FIGS. 5 and 6, the RTP control routine 154 begins with afirst block of codes 162 which directs the processor circuit 66 toproduce display control signals to control the display 70 to prompt auser of the system 20 to either select a pre-defined thermal cycle orinput parameter data defining a new thermal cycle. In response to userinput at the input device 69 indicating a new thermal cycle, theprocessor circuit is directed to prompt the user to input parameter datadefining the desired thermal cycle, including, for example, the totalduration of the thermal cycle, the ramp rate (i.e. the rate at which thetemperature of the workpiece is to be increased), the desired peaktemperature and duration at peak temperature, the desired maximumcooling rate, and the desired temperature distribution (for example, auniform temperature distribution throughout the cycle). The user maychoose to either manually enter the parameter data or insert acomputer-readable storage medium such as a floppy or compact diskcontaining the parameter data into the computer 68 to be read by theprocessor circuit 66. Alternatively, one or more standard sets ofparameters defining thermal cycles desirable for respective standardworkpieces may be stored in the parameter folder 157 in the storagedevice 150, and the user may select a desired pre-defined standardthermal cycle. Such storage of standard sets of parameters is generallypreferable, particularly where a thermal cycle will have to be repeatedor where the desired temperature distribution in the workpiece isnon-uniform or varies over time, in which case it would betime-consuming for a user to manually enter such data. Following suchinput or selection, block 162 directs the processor circuit to load theparameters other than the desired temperature distribution into theparameter store 156 in the RAM 130. Thus, the parameter store willcontain the macroscopic parameters of the thermal cycle, defining theramp rate, maximum temperature and maximum cooling rate, for example.

Block 164 directs the processor circuit to produce, in accordance withthe selected or input parameter data, a representation of a desiredtemperature distribution across the lower surface of the workpiece foreach instant during the thermal cycle at which the temperature of theworkpiece is to be measured. The processor circuit is directed to storeeach such representation in the desired temperature distribution folder159 in the storage device 150.

Block 166 directs the processor circuit to produce display controlsignals to control the display 70 to prompt the user to begin thethermal cycle.

In response to user input at the input device 69 indicating that thethermal cycle is to begin, block 168 directs the processor circuit 66 toproduce primary energy source control signals to activate the primaryenergy source 52 at a power level determined by processor circuit as afunction of the parameter data stored in the parameter store 156,including the desired ramp rate.

Block 170 then directs the processor circuit 66 to copy a representationof the desired temperature distribution corresponding to the nextinstant at which the temperature of the workpiece is to be measured fromthe desired temperature distribution folder 159 into the desiredtemperature distribution store 158.

At block 172, the processor circuit is directed to read the contents ofthe timer store 146 to determine whether a first timer bit has been setactive by a timer subroutine (not shown) to indicate that the thermalcycle is to be ended. If the first timer bit is active, the processorcircuit is directed to produce control signals to deactivate the primaryand corrective energy sources 52 and 60, and the RTP control routine isended.

If at block 172 the first timer bit has not been set active, block 174directs the processor circuit to read the contents of the timer store146 to determine whether a second timer bit has been set active by thetimer subroutine to indicate that the temperature of the workpiece is tobe measured. In this embodiment, the timer subroutine sets active thesecond timer bit once every 100 ms, such that the temperature of theworkpiece is measured at a frequency of ten times per second. However,depending upon the requirements of the particular thermal processingapplication and on the available processing power, the second timer bitmay be set active at a significantly higher or lower frequency. If thesecond timer bit has not been set active, the processor circuitcontinues processing at block 174.

If at block 174 the second timer bit has been set active, block 176directs the processor circuit to reset the second timer bit to zero.

Blocks 178 through 186 then direct the processor circuit to produce anemissivity-compensated representation of the spatial temperaturedistribution across the lower surface of the workpiece.

Block 178 directs the processor circuit 66 to effectively measure theintensity of radiation incident upon the lower surface 35 of theworkpiece 34, and to simultaneously measure the total intensity ofradiation reflected and thermally emitted by the lower surface 35 of theworkpiece 34.

Block 178 first directs the processor circuit to produce secondaryenergy source control signals to deactivate the secondary energy source78 if it had been activated immediately prior to block 178. Theprocessor circuit is then directed to produce sensor control signals tocontrol the radiation sensor 49 to produce sensor signals representingan intensity of incident radiation received from the primary energysource 52 at the radiation sensor. Since the primary energy source 52produces a uniform irradiance field in the vicinity of the lower surfaceof the workpiece, the sensor signals thus represent an intensityI_(incident) of radiation received at each measurement area 110 on thelower surface 35 of the workpiece 34. The sensor signals arecommunicated to the processor circuit 66 through the peripheralinterface 126, and the processor circuit is directed to store thereceived representation of incident intensity incident in the incidentintensity store 131.

Simultaneously with producing the sensor control signals, block 178directs the processor circuit to produce measuring device controlsignals to control the measuring device 62 to cause the CCD 98 tocapture an image of radiation reflected and thermally emitted by thelower surface 35 of the workpiece, for the purpose ofemissivity-compensated temperature measurement. Specifically, the imageof the lower surface 35 of the workpiece 34 captured by the CCD 98 is arepresentation of intensity of radiation reflected and thermally emittedby each of the plurality of measurement areas 110 on the lower surface.The processor circuit is further directed to produce measuring devicecontrol signals to cause the measuring device 62 to produce measurementsignals representing the captured image, which are communicated to theprocessor circuit 66 through the peripheral interface 126. The processorcircuit is then directed to store the representation of intensity ofreflected and thermally emitted radiation so received in the totalradiation store 132.

Immediately thereafter, block 180 directs the processor circuit 66 toeffectively measure the intensity of radiation thermally emitted by theworkpiece The processor circuit is directed to produce primary energysource control signals to momentarily turn off or “notch” the primaryenergy source 52. The secondary energy source 78, having beendeactivated at block 178, remains deactivated. During the notch, theprocessor circuit is directed to produce measuring device controlsignals to control the measuring device 62 to cause the CCD 98 tocapture an image of radiation thermally emitted by the lower surface 35of the workpiece 34, while the workpiece is not being irradiated. Theprocessor circuit is directed to produce further measuring devicecontrol signals to cause the measuring device 62 to produce measurementsignals representing the captured image of intensity of thermallyemitted radiation, which are communicated to the processor circuit 66through the peripheral interface 126. In other words, the measuringdevice 62 acts to produce at least one signal representative ofradiation intensity from the surface of the workpiece.

The processor circuit is then directed to store the representation ofthermal intensity so received in the thermal radiation store 133.

Immediately thereafter (in this embodiment less than one millisecondlater), block 182 directs the processor circuit to produce primary andsecondary energy source control signals to restore the primary andsecondary energy sources 52 and 78 to their respective statesimmediately prior to block 178. Due to the fast response time of the arclamp 54, the total duration of the notch mandated by block 180 isnegligible compared to the time constant for thermal properties of theworkpiece 34 which in this embodiment is a silicon wafer. Thus, thedesired thermal cycle is not significantly affected by the measurementprocess.

Block 184 then directs the processor circuit 66 to produce arepresentation of the emissivity of each of the plurality of measurementareas 110 on the lower surface 35 of the workpiece 34. For each of themeasurement areas 110, the corresponding representation stored in thethermal radiation store 133 is subtracted from the correspondingrepresentation stored in the total radiation store 132, to yield theintensity of radiation reflected by that measurement area just beforethe notch, I_(reflected). This difference is divided by the intensity ofradiation incident upon that area just before the notch, I_(incident),stored in the incident intensity store 131, which is assumed to beuniform for all of the measurement areas 110.

The result of this division represents the reflectivity of thatmeasurement area 110, and is then subtracted from one to yield theemissivity of that measurement area. In other words, the emissivity of aparticular measurement area 110 is defined by $\begin{matrix}{\varepsilon = {\left( {1 - r} \right) = {1 - \frac{I_{reflected}}{I_{incident}}}}} & (1)\end{matrix}$

where

ε= emissivity

r= reflectivity

I_(reflected)= intensity of radiation reflected by the measurement areajust before the notch (difference between corresponding values in totaland thermal radiation stores); and

I_(incident)= intensity of radiation incident upon the measurement areajust before the notch (incident intensity store, constant for eachmeasurement area).

Block 184 directs the processor circuit to store the emissivity valuefor that measurement area into a location in the emissivity store 134 inthe RAM 130 corresponding to that particular measurement area 110. Theabove steps are repeated until an emissivity value has been calculatedand stored in the emissivity store for each one of the plurality ofmeasurement areas 110.

Block 186 then directs the processor circuit 66 to produce arepresentation of an instantaneous spatial temperature distributionacross the lower surface 35 of the workpiece 34. For each one of themeasurement areas 110 on the lower surface 35, a grey-body emissionequation is solved for temperature, by using the value stored in theemissivity store 134 representing the emissivity of that measurementarea and the value stored in the thermal radiation store 133representing the intensity of thermal radiation emitted by that area.For example, the grey-body equation, $\begin{matrix}{I_{thermal} = \frac{2\pi \quad c^{2}h\quad \Delta_{\lambda}\varepsilon}{\lambda^{5}\left( {^{{{hc}/\lambda}\quad {kT}} - 1} \right)}} & (2)\end{matrix}$

may be solved to yield $\begin{matrix}{T = \frac{hc}{\lambda \quad k\quad {\ln \left( {1 + \frac{2\pi \quad c^{2}h\quad \Delta_{\lambda}\varepsilon}{I_{thermal}\lambda^{5}}} \right)}}} & (3)\end{matrix}$

 where

T= temperature of the workpiece measurement area 110

I_(thermal)= intensity of radiation thermally emitted by the measurementarea at wavelength λ (from the corresponding location in the thermalradiation store 133)

ε= emissivity of the measurement area 110 (from the correspondinglocation in the emissivity store 134)

λ= wavelength at which I_(thermal) was measured (in this embodiment,λ=900 nm)

Δ_(λ)= bandpass of the measuring device (in this embodiment, ±5 nm)

c= speed of light

h= Planck's constant

k= Boltzmann's constant

e= Euler's number

The only variables are emissivity ε and thermal intensity I_(thermal).Thus, for each of the measurement areas 110, the correspondingemissivity value and thermal intensity value stored in the emissivitystore and thermal radiation store respectively are used to solveEquation (3) for temperature T.

The resulting value representing the temperature of that particularmeasurement area 110 is then stored by the processor circuit 66 in alocation in the temperature store 136 corresponding to that measurementarea. The processor circuit is directed to repeat the above calculationfor all of the measurement areas 110, and thus a representation of thespatial temperature distribution across the entire lower surface 35 ofthe workpiece is produced by the processor circuit and stored in thetemperature store 136. In effect, the processor circuit 66, measuringdevice 62 and radiation sensor 49 act as a measuring system forproducing a representation of an instantaneous spatial temperaturedistribution in the workpiece, and the temperature store 136 acts as astorage medium in communication with the processor circuit for storingthe representation of the instantaneous spatial temperaturedistribution.

Blocks 188 through 198 then direct the processor circuit to cooperatewith the corrective energy source 60 and primary energy source 52 tocounteract any deviations or errors from the desired temperaturedistribution in the workpiece. Block 188 directs the processor circuitto produce an instantaneous spatial temperature error distributionrepresentation, representing an error between desired and actualtemperature across the entire lower surface 35 of the workpiece 34. Foreach measurement area 110, the processor circuit is directed to read thedesired temperature of that measurement area stored in a location of thedesired temperature distribution store 158 corresponding to thatmeasurement area, and to read the actual temperature of that measurementarea stored in the location of the temperature store 136 correspondingto that measurement area. The processor circuit is directed to subtractthe desired temperature from the actual temperature to produce atemperature error value, and to store the temperature error value in alocation of the temperature error store 138 corresponding to thatmeasurement area. Thus,t the processor circuit is programmed to controlthe measuring system to produce an instantaneous spatial temperatureerror distribution as a function of the desired spatial temperaturedistribution and the instantaneous spatial temperature distribution.

It will be appreciated that the temperature error value will be negativeif the actual temperature of the measurement area is cooler than itsdesired temperature, and positive if the measurement area is hotter thandesired. The processor circuit is directed to repeat the above stepsuntil temperature error values for all of the measurement areas 110 havebeen calculated and stored in the temperature error store 138.

Block 190 directs the processor to produce a corrective powerrepresentation of a corrective irradiance image to be projected onto thelower surface 35 of the workpiece by the corrective energy source 60, inorder to counteract the temperature errors. The corrective powerrepresentation comprises a two-dimensional array of correction values.Each of the correction values is a whole number corresponding to adiscrete shade of grey available on the LCD panel 82 in the correctiveenergy source 60, and thus, each correction value represents a variableopacity of an LCD image producing pixel 86 corresponding to a particularprojection area 96 on the lower surface 35 of the workpiece. In thisembodiment, the number zero corresponds to the darkest shade of grey(black or opaque) and the number 15 corresponds to the lightest shade ofgrey (transparent).

Block 190 directs the processor circuit to locate the highest and lowesttemperature error values in the temperature error store 138, and toassign correction values of 0 and 15 to the highest and lowesttemperature error values respectively. For each of the projection areas96 on the lower surface, the processor circuit is directed to calculatean average of the temperature error values stored in the locations inthe temperature error store 138 corresponding to the particularmeasurement areas 110 into which the particular projection area 96 issubdivided. The processor circuit is then directed to convert thecalculated average temperature error value of the projection area 96into a correction value between 0 and 15, representing one of thepossible shades of grey of the corresponding pixel of the LCD. Theconversion is a function of the difference between the highest andlowest temperature error values. The foregoing calculation of correctionvalues is illustrated by way of example in FIGS. 7A through 7C, whichare discussed in further detail following block 198 below.

The processor circuit is directed to store each correction value in thelocation of the corrective power store 140 corresponding to theparticular projection area 96, and is then directed to repeat the abovesteps until correction values have been stored for all the projectionareas 96 on the lower surface 35 of the workpiece.

Block 194 the directs the processor circuit to produce secondary energysource control signals to activate the secondary energy source 78 toproject a corrective irradiance image through the LCD panel 82 and theLCD imaging optics system 84 onto the lower surface 35 of the workpiece.The secondary energy source control signals control the secondary energysource to irradiate at a power level proportional to the temperaturedifference between the highest and lowest temperature error values. Thesecondary energy source 78 thus acts to direct radiation to the surface.

Immediately thereafter, block 196 directs the processor circuit toselectively vary the opacity of each of the image producing pixels 86 onthe LCD panel 82, to selectively irradiate corresponding projectionareas 96 on the lower surface 35 of the workpiece. For each of theprojection areas 96, the processor circuit is directed to produce LCDimage producing pixel control signals to control the image producingpixel corresponding to the particular projection area to assume a shadeof grey determined by the corresponding correction value stored in thecorrective power store 140. For example, if the correction valuecorresponding to a particular projection area is zero, the processorcircuit renders the corresponding image producing pixel black or opaque.If the correction value is 15, the processor circuit renders thecorresponding image producing pixel transparent. For intermediatecorrection values, the image producing pixels are controlled to assumerespective discrete shades of grey. The above step is repeated until theprocessor circuit has produced and provided LCD image producing pixelcontrol signals to control all of the image producing pixels 86. Ineffect, the LCD panel 82 acts as a filtering member interposed betweenthe secondary energy source and the lower surface of the workpiece, thefiltering member having a plurality of filter portions, each of theplurality of filter portions having a variable opacity, and theprocessor circuit is programmed to selectively vary, as a function ofthe representation of the spatial temperature distribution across theworkpiece, the variable opacity of each of the plurality of filterportions, thereby producing the desired spatial temperature distributionin the workpiece. The processor circuit is thus programmed to varyirradiance produced by at least one of the primary and corrective energysources.

Thus, at this point in the thermal cycle, the secondary energy source 78and the reflector 80 project radiation toward the LCD panel 82. Each ofthe LCD image producing pixels 86 has a variable opacity, as determinedby the corrective power representation, and radiation passing througheach image producing pixel 86 is projected through the LCD imagingoptics system 84 onto a particular corresponding projection area 96 onthe lower surface of the workpiece. Thus, a corrective irradiance imageof the LCD panel 82 is projected onto the workpiece. The correctiveenergy source 60 thus acts as an irradiance system for irradiating aplurality of areas on a surface of the workpiece to create localizedheating of the workpiece in the areas, to change the spatial temperaturedistribution to produce the desired spatial temperature distribution inthe workpiece. The processor circuit is in communication with theirradiance system, and is programmed to control the irradiance system,particularly the LCD panel, to expose each one of the plurality of areasto radiation to produce the localized heating. In effect, the processorcircuit is programmed to control the irradiance system, or moreparticularly, the LCD panel, to control the amount of the localizedheating by irradiating in response to the instantaneous spatialtemperature error distribution. This is done by using the LCD panel tocontrol the amount of radiation to which each of the areas is exposed,or to control the exposure of each of the areas to radiation.

Block 198 directs the processor circuit 66 to adjust the power of theprimary energy source 52, in order to provide any macroscopicadjustments which may be required to produce the desired temperaturedistribution. It will be appreciated that the corrective irradianceimage produced by the corrective energy source 60 can increase ordecrease temperatures of the projection areas 96 on the workpiecerelative to each other, but cannot reduce the absolute temperature of aprojection area which is hotter than its desired temperature. Also, thecorrective irradiance image produced by the corrective energy source maycause the average temperature of the workpiece to increase beyond itsdesired average temperature. In such cases it is desirable to reduce thepower projected onto the workpiece by the primary energy source.Conversely, if the entire workpiece falls significantly below itsdesired temperature, it may be desirable to increase the power projectedby the primary energy source.

Thus, block 198 directs the processor circuit to produce primary energysource control signals to adjust the power projected by the primaryenergy source 52 onto the workpiece. The processor circuit is directedto determine the magnitude of the power adjustment as a function of boththe average power being projected onto the workpiece by the correctiveenergy source 60, and of the highest temperature error value stored inthe temperature error store 138. For example, if the highest temperatureerror value is positive (indicating that the corresponding measurementarea 110 of the workpiece is hotter than its desired temperature), theeffect of block 198 would be to proportionally reduce the powerprojected by the primary energy source onto the workpiece. Conversely,if the highest temperature error value is negative and is less than apre-defined value (such as −0.5, for example, indicating that everymeasurement area 110 is at least 0.5° C. cooler than its desiredtemperature), the effect of block 198 would be to increase the powerprojected by the primary energy source onto the workpiece. Thus, themeans for irradiating includes means for varying irradiance produced byat least one of the primary and corrective means for irradiating.

Referring to FIGS. 6, 7A, 7B and 7C, a hypothetical example of blocks186 to 198 is shown. It is assumed for simplicity that the desiredtemperature distribution is a uniform temperature of 1040° C. at allmeasurement areas 110 on the lower surface 35.

FIG. 7A illustrates a spatial temperature distribution across a verticalcross-section of the workpiece, ranging from 1039.00° C. to 1040.50° C.,as calculated at block 186. The resulting temperature error distributioncalculated at block 188 would thus contain temperature error valuesranging from ±0.50 to −1.00. At block 190, a correction value of zerowould be assigned to any of the projection areas 96 having an averagetemperature error of ±0.5 (or in other words, an average temperature of1040.5° C.), a correction value of 2 would be assigned to any projectionarea 96 having an average temperature error of ±0.3, a correction valueof 6 would be assigned to any projection area 96 having an averagetemperature error of zero (average temperature of 1040.0° C.) , acorrection value of 12 would be assigned to any projection area 96having an average temperature of −0.7 (average temperature of 1039.3°C.), a correction value of 15 would be assigned to any projection area96 having an average temperature error of −1.0 (average temperature of1039° C.), and so on. Block 194 would then direct the processor circuitto activate the secondary energy source 78 to project radiation throughthe LCD panel 82 and the LCD imaging optics system 84 onto the lowersurface of the workpiece. For each of the projection areas 96 on theworkpiece, block 196 would direct the processor circuit to control theLCD image producing pixel 86 corresponding to that projection area toassume an opacity or shade of grey determined by the correction valuecorresponding to that projection area: LCD image producing pixels withcorresponding correction values of zero would be opaque to the radiationprojected by the secondary energy source, while image producing pixelswith corresponding correction values of 15 would be essentiallytransparent. Thus, the corrective energy source would project virtuallyno radiation onto the projection area(s) having a correction value ofzero (temperature of 1040.5° C.), and would project the greatestintensity of radiation onto the projection area(s) having a correctionvalue of 15 (temperature of 1039.0° C.).

Referring to FIGS. 6 and 7B, it will be appreciated that in thisexample, blocks 190 to 196 would tend to increase the temperature of allprojection areas toward the temperature of the hottest areas on theworkpiece (temperature of 1040.5° C., correction value zero). In otherwords, in this example, blocks 190 to 196 tend to “flatten” thetemperature curve. More generally, blocks 190 to 196 cause thetemperature curve to tend to assume the relative shape of the desiredtemperature distribution curve.

Referring to FIGS. 6 and 7C, in this example, block 198 would direct theprocessor circuit to reduce the power projected onto the workpiece bythe primary energy source 52, resulting in greater net cooling (or moregenerally, reduced net heating) of the workpiece. In other words, theprimary energy source power adjustment at block 198 tends to “shift” theflattened temperature curve as a whole, toward an average value of thedesired temperature distribution.

Referring back to FIG. 6, block 200 then directs the processor circuitto graphically display desired information on the display 70. In thisembodiment, the desired information is the temperature errordistribution stored in the temperature error store 138. Block 200directs the processor circuit to sequentially read the temperature errorvalues in the temperature error store 138 corresponding to each of themeasurement areas 110 on the lower surface 35 of the workpiece. For eachof the measurement areas 110, the processor circuit is directed toproduce a colour value as a function of the corresponding temperatureerror value and store the colour value in a corresponding location inthe display store 142. Each colour value represents one of a pluralityof discrete shades of red, orange, yellow, green, blue or violetavailable on the display 70. In this embodiment, the processor circuitis directed to produce a colour value representing theshortest-wavelength shade of violet available on the display for anytemperature error values greater than or equal to +3.00° C., a colourvalue representing the longest-wavelength shade of red available on thedisplay for any temperature error values less than or equal to −3.00°C., and to produce colour values representing intermediate colours whichrange from red to orange to yellow to green to blue to violet fortemperature error values ranging from −3.00° C. to +3.00° C.respectively. Once all such colour values have been stored in thedisplay store 142, block 200 directs the processor circuit to producedisplay control signals to cause the display 70 to display the contentsof the display store 142.

Referring back to FIG. 1, for each of the measurement areas 110 of theworkpiece, the processor circuit controls a corresponding display pixel71 on the display 70 to emit the colour represented by the colour valuestored in the corresponding location in the display store 142.Alternatively, depending on user preferences, representations of thecontents of any of the various stores in the RAM 130 may be displayed bya similar colour assignment process, and different colour conversionscales may be used for any such displays.

Block 202 then directs the processor circuit to store the contents ofthe temperature store 136 in the archive folder 160 in the storagedevice 150, thus maintaining a record of the spatial temperaturedistribution across the lower surface of the workpiece at each point intime during the thermal cycle at which temperature was measured.Alternatively, however, depending on user preferences, any of theinformation contained in the various stores in the RAM 130 may berecorded in the storage device 150.

The processor circuit is then directed back to block 170, which directsthe processor circuit to copy a representation of the desiredtemperature distribution corresponding to the next instant at which thetemperature of the workpiece is to be measured from the desiredtemperature distribution folder 159 into the desired temperaturedistribution store 158.

Thereafter, the processor circuit repeats the above steps of blocks 170to 202 for each successive desired temperature distribution, and thethermal cycle thus continues until such time as the processor circuitdetermines at block 172 that the first timer bit has been set active bythe timer subroutine, and terminates the thermal cycle in responsethereto.

Thus, the foregoing describes one embodiment of a system for producing adesired spatial temperature distribution across a workpiece. Theprocessor circuit cooperates with the chamber, the measuring device andprimary energy source to produce a representation of the spatialtemperature distribution across the workpiece, which is compared to thedesired temperature distribution. The processor circuit then cooperateswith the primary and corrective energy sources to act as an irradiancesystem for irradiating a plurality of areas on a surface of theworkpiece to create localized heating of the workpiece in those areas,to produce the desired spatial temperature distribution in theworkpiece.

Alternatives Primary Energy Source

The primary energy source 52 need not be an arc lamp. An alternativeenergy source, such as a plurality of tungsten lamps, for example, couldbe substituted for the arc lamp 54. Although tungsten lamps and otheralternative energy sources may lack the advantages discussed aboveresulting from the short wavelength and fast response time of the arclamp, such alternative energy sources may still provide sufficientefficiency and response time for many thermal processing applications.

As a further alternative, the primary energy source may be removedentirely, and the corrective energy source 60 may therefore act as thesole energy source heating the workpiece, depending upon the energyrequired to heat the workpiece to the desired temperature.

As shown in FIG. 8, a system for producing a desired spatial temperaturedistribution across a workpiece according to a second embodiment of theinvention is designated generally by the reference character 210. Thesystem 210 differs from the system 20 shown in FIG. 1 in that theprimary energy source 52 has been removed, and the second angled window50 has been replaced with a fourth lower angled wall 212. The fourthlower angled wall 212 includes radiation-absorbing material, which inthis embodiment is black stainless steel, and thus acts as aradiation-absorbing surface. The secondary energy source 78 has beenreplaced with a sole energy source 214 capable of irradiating theworkpiece with sufficient power to carry out a desired thermal cycle.

The LCD panel (82) has been replaced with a finer-greyscale LCD panel216 which includes a plurality of LCD image producing pixels 218. Inthis embodiment, each of the image producing pixels has a greyscale of256 shades of grey, represented by the numbers 0 (opaque) to 255(transparent). The finer-greyscale LCD panel 216 enables the sole energysource to provide the desired ramp rate by delivering significantamounts of power to areas of the workpiece which are hotter thandesired, while providing even higher amounts of power to areas of theworkpiece which are cooler than desired. For example, in a hypotheticalthermal cycle, the processor circuit might render an LCD image producingpixel 218 corresponding to the hottest projection area 96 on theworkpiece partially transparent (rather than opaque), and render thepixel corresponding to the coolest projection area fully transparent.

Similarly, each of the various alternative corrective energy sourcesdiscussed below may be used as a sole energy source if desired.

Corrective Energy Source

Referring to FIG. 9, a corrective energy source according to a thirdembodiment of the invention is shown generally at 220. The correctiveenergy source 220 has a body 222 and a focal barrel 224 mounted beneaththe first angled window 48. Housed within the body is an irradiancesource 225 for directing radiation, which in this embodiment includes anarc lamp 226 and a reflector 228. Thus, the irradiance source acts as atleast one energy source. The irradiance source and reflector projectradiation toward a reflective panel 230, which in this embodiment is areflective LCD panel.

The reflective panel 230 differs from the LCD panel 82 of the firstembodiment, in that it has a rear surface 231 (distal from theworkpiece) coated with a highly reflective material. When the processorcircuit 66 produces electrical image control signals to render a givenLCD element or pixel of the reflective panel transparent, radiationincident upon that pixel passes through the pixel, strikes the rearsurface 231, and is reflected, essentially undiminished (subject tominimum inherent power loss of an LCD panel). Conversely, when theprocessor circuit renders a given pixel opaque, radiation incident uponthe pixel will be absorbed by the pixel, and when the processor circuitcauses a pixel to assume an intermediate shade of grey, radiationincident upon that pixel will be partly absorbed by the pixel and partlyreflected back through the pixel by the rear surface 231. Thus, ineffect, the reflective panel 230 includes a plurality of image producingpixels, each of which has a variable reflectivity.

An imaging optics system 232 is housed within the focal barrel 224, andis operable to project an image of the reflective panel 230 onto thelower surface 35 of the workpiece 34, such that each of the imageproducing pixels on the reflective panel corresponds to a particularprojection area 96 on the lower surface of the workpiece. Thus, thereflective panel 230 acts to reflect the radiation from the irradiancesource 225 to the surface of the workpiece.

In this embodiment, the processor circuit 66 produces corrective energysource control signals to selectively control each of the imageproducing pixels on the reflective panel 230 to assume a discretereflectivity value, as determined by the corresponding correction valuestored in the corrective power store 140. Radiation projected onto thereflective panel by the irradiance source 225 is thus selectivelyreflected by the reflective panel 230 through the imaging optics system232 onto each of the projection areas on the lower surface 35 of theworkpiece 34. Thus, the irradiance system includes a reflecting memberoriented to reflect radiation incident from the at least one energysource to the surface, the reflecting member having a plurality ofreflector portions, each of the plurality of reflector portions having avariable reflectivity. The processor circuit is programmed toselectively vary, as a function of the representation of the spatialtemperature distribution across the workpiece, the variable reflectivityof each of the plurality of reflector portions of the reflecting member,thereby producing the desired spatial temperature distribution in theworkpiece.

Any suitable array of reflective elements each having a variablereflectivity may be substituted for the reflective LCD panel.

Referring to FIG. 10, a corrective energy source according to a fourthembodiment of the invention is shown generally at 240. The correctiveenergy source 240 includes a first body portion 242, a second bodyportion 244, and a focal barrel 246 mounted beneath the first angledwindow 48. Housed within the first body portion 242 is an irradiancesource 247 for directing radiation, which in this embodiment includes areflector 248 and an arc lamp 250. The arc lamp and reflector cooperateto project radiation through an integrator 252 into a condenser 254housed within the second body portion. The condenser 254 condenses andprojects the radiation onto a Schlieren stop 256 in the focal barrel246, which reflects the radiation through a Schlieren lens 258 onto areflective panel 260, which in this embodiment is a reflective LCD panelsimilar to the reflective panel 230 previously described. The reflectivepanel 260 includes a plurality of reflective LCD pixels or imageproducing pixels. Radiation reflected by the image-producing pixelspasses back through the Schlieren lens 258 and through a projection lens262, which projects an image of the reflective panel 260 onto the lowersurface 35 of the workpiece 34, such that each image producing pixelcorresponds to a particular projection area 96 on the lower surface ofthe workpiece.

The processor circuit produces reflector control signals to selectivelyvary the reflectivity of each of the image producing pixels toselectively vary the intensity of radiation projected onto each of theprojection areas 96 on the workpiece.

Referring to FIG. 11, a corrective energy source according to a fifthembodiment of the invention is shown generally at 270. Housed within abody 272 of the corrective energy source is an array of energy sourcesor irradiance sources 274 for projecting radiation onto the lowersurface of the workpiece. The irradiance sources may includelight-emitting diodes or laser diodes, for example.

Alternatively, any other suitable array of irradiance sources, such asan array of lasers or an array of tungsten lamps, for example, may besubstituted. An imaging optics system 276 is housed within a focalbarrel 278 mounted beneath the first angled window 48. The array ofirradiance sources projects radiation through the imaging optics system276, which projects an image of the array onto the lower surface 35 ofthe workpiece 34, such that each one of the irradiance sources 274projects radiation onto a particular projection area 96 on the lowersurface 35 of the workpiece 34. The processor circuit 66 producesirradiance control signals to selectively vary the power projected byeach one of the irradiance sources 274 onto each correspondingprojection area 96 on the lower surface of the workpiece. Thus, theprocessor circuit 66 acts to selectively vary, as a function of therepresentation of the spatial temperature distribution across theworkpiece, an intensity of radiation emitted by each of the energysources or irradiance sources 274. The imaging optics system 276provides at least one lens interposed between the array of energysources and the workpiece.

As shown in FIGS. 12 and 13, a system for producing a desired spatialtemperature distribution across a workpiece according to a sixthembodiment of the invention is designated generally by the referencecharacter 280. The corrective energy source 60 shown in FIG. 1 has beenremoved and replaced with a corrective energy source 282 mounted in theupper portion 24 of the chamber 22, centred directly above and parallelto the workpiece 34. In this embodiment, the corrective energy source282 includes an array of infrared reflector panels 284 for reflectingradiation thermally emitted by the workpiece surface back to thesurface. Each of the infrared reflector panels 284 has a variablereflectivity, and is operable to reflect infrared radiation thermallyemitted by a particular corresponding reflection area 286 on the uppersurface 33 of the workpiece 34 back to that corresponding reflectionarea 286. In this embodiment, the correction values stored in thecorrective power store 140 shown in FIG. 5 correspond to particularreflection areas 286 on the upper surface 33, each reflection areacorresponding to a plurality of measurement areas 110 on the lowersurface 35. For each of the reflection areas 286, the processor circuit66 produces infrared reflector control signals to control thecorresponding infrared reflector panel 284 to assume a degree ofreflectivity proportional to the corresponding correction value. Inother words, the irradiance system includes a reflecting member forreflecting radiation thermally emitted by the surface back to thesurface, the reflecting member having a plurality of reflector portions,each of the plurality of reflector portions having a variablereflectivity. The processor circuit is programmed to selectively vary,as a function of the representation of the spatial temperaturedistribution across the workpiece, the variable reflectivity of each ofthe plurality of reflector portions, thereby producing the desiredspatial temperature distribution in the workpiece. Thus the processorcircuit is operable to selectively vary the intensity or amount ofthermally emitted infrared radiation reflected back to each of thereflection areas 286 on the upper surface of the workpiece.

Referring to FIG. 14, a corrective energy source according to a seventhembodiment of the invention is shown generally at 290. The correctiveenergy source 290 includes a scanning laser 292 for scanning a laserbeam 294 across the entire lower surface 35 of the workpiece 34. Thescanning laser 292 includes a scan circuit (not shown) which operates ona similar principle to a raster scan circuit for a television set. Theprocessor circuit 66 produces laser control signals to cause the laserbeam 294 to remain incident upon each one of a plurality of laserprojection areas 296 on the lower surface of the workpiece for a timeperiod determined by a correction value corresponding to that particularlaser projection area 296, stored in the corrective power store 140.Thus, the laser beam 294 will quickly scan over the laser projectionareas 296 which are hottest relative to their desired temperature, butwill remain incident upon cooler areas for proportionally longer periodsof time, thus providing greater heating of such cooler areas. In otherwords, the processor circuit is programmed to selectively vary, as afunction of the representation of the spatial temperature distributionacross the workpiece, a time during which the laser beam remainsincident upon the surface in the vicinity of each of the laserprojection areas respectively.

Alternatively, the laser beam may remain incident on each laserprojection area 296 for an equal period of time, and the processorcircuit may selectively control the power of the laser beam as it scansacross each of the laser projection areas 296. Thus, the processorcircuit is programmed to selectively vary, as a function of therepresentation of the spatial temperature distribution, a power of thelaser beam in the vicinity of each of the laser projection areasrespectively.

Measuring Device

Referring to FIG. 15, a measuring device according to an eighthembodiment of the invention is shown generally at 300. The measuringdevice 300 includes a linear detector 302, a movable mirror 304, amirror motion assembly 306, and an optics system 308 illustrated byrepresentative lenses in FIG. 15. A filter 310 within the measuringdevice is interposed between the optics system and the workpiece. Theoptics system 308 and the movable mirror 304 cooperate to focus andreflect radiation emitted or reflected by a particular measurement area110 of the lower surface 35 to the linear detector 302. In thisembodiment, the mirror motion assembly 306 operates on a similarprinciple to an alt-azimuth mounting assembly of a telescope, althoughon a much smaller and faster scale. Alternatively, any other suitablemotion assembly may be substituted therefor. The processor circuit 66produces mirror control signals to control the mirror motion assembly306 to cause the movable mirror to move incrementally, thus reflectingradiation emitted or reflected by successive measurement areas 110 onthe lower surface of the workpiece into the linear detector. With eachincremental movement of the mirror, the processor circuit producesdetector control signals to cause the linear detector to sequentiallymeasure radiation emitted or reflected from each of the successiveadjacent measurement areas 110. In this manner, the processor circuitproduces mirror control signals to effectively control the lineardetector to perform a raster scan across the entire lower surface of theworkpiece, by moving the mirror rather than the detector. In otherwords, the measuring system includes a detector, a movable mirror and amirror control device (the mirror motion assembly) in communication withthe processor circuit. The processor circuit is programmed to controlthe mirror control device to move the mirror among a plurality of mirrorpositions, each of the mirror positions corresponding to a respectiveone of the areas on the surface of the workpiece, thereby reflecting tothe detector radiation from each of the areas respectively. The opticssystem 308 provides at least one lens interposed between the movablemirror and the workpiece, and at least one lens interposed between thedetector and the movable mirror.

Referring to FIG. 16, a measuring device according to a ninth embodimentof the invention is shown generally at 312. The measuring deviceincludes a linear detector 314, a detector motion assembly 316 and animaging optics system 318. The processor circuit 66 controls thedetector motion assembly 316 to move the linear detector among aplurality of detector positions, each of the detector positionscorresponding to a respective measurement area 110 on the lower surfaceof the workpiece, so that the detector receives radiation from each ofthe measurement areas. Thus, in this embodiment, the measuring systemincludes a detector and a detector control device (the detector motionassembly) in communication with the processor circuit. The processorcircuit is programmed to control the detector control device to move thedetector among a plurality of detector positions, each of the detectorpositions corresponding to a respective one of the areas on the surfaceof the workpiece, thereby receiving at the detector radiation from eachof the areas respectively. The imaging optics system 318 provides atleast one lens interposed between the detector and the workpiece.

Referring to FIG. 17, a measuring device according to a tenth embodimentof the invention is shown generally at 320. The measuring device 320 hasa body 322 in which is housed an array of sensors 324, which in thisembodiment is an array of photo diodes. The measuring device 320 alsohas a focal barrel 326 in which is housed an imaging optics system 328,which projects an image of the lower surface 35 of the workpiece ontothe array of sensors 324, such that radiation from each one of aplurality of sensor areas 330 on the lower surface 35 of the workpieceis projected onto a particular corresponding one of the sensors 324. Themeasuring device 320 cooperates with the processor circuit toeffectively measure temperature as described above. Thus, in thisembodiment, the measuring system includes at least one radiationdetector (the array of sensors), and at least one lens (the imagingoptics system) interposed between the workpiece and the at least oneradiation detector. This embodiment is particularly useful forlower-temperature applications, since photo diodes, although lacking theresolution of a CCD, are generally well-suited to measuring lowertemperatures.

Alternatively, a smaller number of sensors may be combined with themirror motion assembly 306 and the movable mirror 304 shown in FIG. 15or the motion assembly shown in FIG. 16, resulting in a scanning arrayof sensors operable to scan across the lower surf ace of the workpiece.

In any of the embodiments described herein, the band-pass filter 100shown in FIG. 1 need not have a band pass of λ=900±5 nm, and indeed,this band-pass may not be suitable for lower-temperature applications,for which a longer measurement wavelength may be required.

Processor Circuit

The processor circuit need not be housed within a general purposecomputer. Alternatively, for example, a microcontroller in communicationwith the measuring device and all energy sources may be housed withinthe measuring device, or may be located at any other suitable locationin the system. The RTP control routine and standard sets of parametersmay be stored in a storage medium accessible by the microcontroller,such as electrically-erasable programmable read-only memory (EEPROM) orFLASH memory, for example.

RTP Control Routine

Although emissivity may vary from measurement area 110 to measurementarea across the lower surface 35 of the workpiece, emissivity variesonly weakly with temperature, and thus emissivity varies relativelyslowly during a rapid thermal processing cycle. Thus, if it is desirableto conserve processing power, emissivity may be measured and calculatedless frequently than temperature. For example, total (reflected+thermal)radiation might be measured and stored to determine emissivity only onceper second during the thermal cycle, and emissivity may be assumed to beconstant over the intervening second in order to calculate temperaturefrom the more frequent measurements of thermal radiation.

In thermal cycles where the desired temperature distribution is auniform temperature distribution throughout the workpiece at all timesduring the thermal cycle, processing power may be further conserved byeliminating the need to produce representations of desired temperaturedistributions or to compare the representations of actual spatialtemperature distribution thereto. Referring back to FIG. 6, in aneleventh embodiment of the invention, blocks 170 and 188 may beeliminated, and the corrective power representation may be calculated ata modified block 190 directly from the contents of the temperaturestore. Where a 16-shade greyscale LCD is used, the modified block 190directs the processor circuit to assign the number zero to the hottestmeasurement area 110, the number 15 to the coolest measurement area, andintermediate numbers to respective measurement areas with intermediatetemperatures. For each projection area 96, the processor circuitaverages the numbers so assigned to the measurement areas 110 comprisedby the projection area, rounds the result to the nearest whole numberand stores the rounded result in the corrective power store.

Additionally, in some cases, it may be desirable to factor out theband-pass and sensor response from equation (3) before calculatingtemperature. To achieve this, in a twelfth embodiment of the invention,a reference object (not shown) at a fixed temperature T_(ref) with knownemissivity ε_(ref) may be placed in the chamber in the field of view ofthe measuring device, and simultaneous measurements of intensity ofthermal radiation of the reference object and the workpiece, I_(ref) andI_(w), may be obtained in a single image. Since both the referenceobject and workpiece simultaneously obey equation (2), the simultaneousequations for the reference object and the workpiece may be solved toyield $\begin{matrix}{T = \frac{hc}{\lambda \quad k\quad {\ln \left\lbrack {\frac{I_{ref}\varepsilon_{w}}{I_{w}\varepsilon_{ref}}\left( {^{{{hc}/\lambda}\quad {kT}_{ref}} - 1} \right)} \right\rbrack}}} & (4)\end{matrix}$

where

T= temperature of the workpiece measurement area 110

I_(ref)= intensity of radiation thermally emitted by the referenceobject

I_(w)= intensity of radiation thermally emitted by workpiece measurementarea 110

ε_(W)= emissivity of the workpiece measurement area 110

ε_(ref)= known emissivity of the reference object

T_(ref)= fixed temperature of the reference object

λ= wavelength at which I_(w) and I_(ref) were measured (in thisembodiment, λ=900 nm)

c= speed of light

h= Planck's constant

k= Boltzmann's constant

e= Euler's number

Finally, in some cases it may be desirable to measure temperature via analternative “flash” procedure, wherein the intensity of radiationreflected by the lower surface 35 of the workpiece is measured by“flashing” the workpiece at a predetermined power level sufficientlyhigh that the intensity of radiation thermally emitted by the workpieceis negligible compared to the intensity of radiation reflected by theworkpiece during the flash.

Referring back to FIG. 6, in a thirteenth embodiment of the invention,block 178 has been modified to direct the processor circuit 66 toeffectively measure an intensity of radiation reflected by the lowersurface 35 of the workpiece 34 during a flash at a pre-determinedintensity produced by the primary energy source 52. Modified block 178directs the processor circuit to produce secondary energy source controlsignals to deactivate the secondary energy source 78 if it had beenactivated immediately prior to block 178. The processor circuit is thendirected to produce primary energy source control signals to control theprimary energy source to produce a “flash” at the pre-determined powerlevel. Due to the fast response time of the arc lamp 54, the arc lampmay easily be controlled to create a sufficiently short flash (less thanone millisecond, for example) that the desired thermal cycle will not beappreciably affected by the flash. In this embodiment, thepre-determined power of the flash is also such that the intensity ofradiation thermally emitted by the workpiece at its maximum temperaturein a thermal cycle at the wavelength (λ=900±5 nm) of the band-passfilter 100 of the measuring device is negligible compared to theintensity of radiation reflected by the workpiece during the flash, andmay be ignored. Simultaneously with the flash, the processor circuit isdirected to produce measuring device control signals to control themeasuring device 62 to cause the CCD 98 to capture an image of radiationreflected by the lower surface 35, or in other words, a representationof reflected intensity of the workpiece 34 during the “flash”, for thepurpose of emissivity-compensated temperature measurement. The image ofthe lower surface 35 of the workpiece 34 captured by the CCD 98 duringthe flash is a representation of intensity of radiation reflected byeach of the plurality of measurement areas 110 on the lower surfaceduring the flash. The processor circuit is further directed to producemeasuring device control signals to cause the measuring device 62 toproduce measurement signals representing the captured image of reflectedintensity, which are communicated to the processor circuit 66 throughthe peripheral interface 126. The processor circuit is then directed tostore the representation of reflected intensity so received in the totalradiation store 132.

Blocks 180 and 182 direct the processor circuit to perform the samesteps as described in the context of the first embodiment of theinvention.

A modified block 184 then directs the processor circuit 66 to produce arepresentation of the emissivity of each of the plurality of measurementareas 110 on the lower surface 35 of the workpiece 34. Since theintensity of radiation thermally emitted by the workpiece during the“flash” is negligible compared to the intensity of radiationsimultaneously reflected by the workpiece, the value stored in the totalradiation store 132 already represents the intensity I_(reflected) ofradiation reflected by the corresponding measurement area 110.Accordingly, in this embodiment it is unnecessary to subtract the valuestored in the corresponding location in the thermal radiation store 133.Thus, for each of the measurement areas 110, the correspondingrepresentation stored in the total radiation store 132 is divided by theintensity of radiation incident upon that area during the flash. Sincethe flash was at a pre-determined power level, the incident intensityduring the flash is a known constant for each of the measurement areas110, and is stored as data within the modified RTP control routine 154.Thus, in this embodiment the radiation sensor 49 is unnecessary. Theresult of this division represents the reflectivity of that measurementarea 110, and is then subtracted from one to yield the emissivity ofthat measurement area. Modified block 184 directs the processor circuitto store the emissivity value for that measurement area into a locationin the emissivity store 134 in the RAM 130 corresponding to thatparticular measurement area 110. The above steps are repeated until anemissivity value has been calculated and stored in the emissivity storefor each one of the plurality of measurement areas 110. The remainder ofthe RTP control routine proceeds as described above.

Although the “flash” procedure conserves processing power by eliminatingboth a calculation step (subtraction of thermal intensity from total(reflected+thermal) intensity) and a measurement step (incidentintensity as measured by the radiation sensor 49), it requires ahighly-powerful “flash” for higher-temperature thermal processing. Also,since incident intensity is inferred from the pre-determined power levelof the flash rather than directly measured, an additional source ofmeasurement error may he introduced if the primary energy source is notprecisely calibrated. To address these difficulties, the “flash”procedure may be further modified so that incident intensity is measuredby the radiation sensor 49, as described above in the context of thefirst embodiment. Also, to avoid the necessity of producing anoverly-powerful flash, the RTP control routine may be further modifiedto use a lower-power “flash” measurement procedure in thelower-temperature stages of a thermal cycle, or perhaps only to producean initial room-temperature measurement of emissivity and temperature,and to revert to the measurement procedure described in the context ofthe first embodiment for the higher-temperature stages of the thermalcycle.

While specific embodiments of the invention have been described andillustrated, such embodiments should be considered illustrative of theinvention only and not as limiting the invention as construed inaccordance with the accompanying claims.

What is claimed is:
 1. A method for producing a desired spatialtemperature distribution across a workpiece, comprising irradiating aplurality of areas on a surface of the workpiece in response to arepresentation of a temperature distribution as a function of at leasttwo independent spatial variables across the workpiece, to createlocalized heating of the workpiece in said areas, to produce the desiredspatial temperature distribution in the workpiece.
 2. A method asclaimed in claim 1 wherein irradiating includes exposing each one ofsaid plurality of areas to radiation to produce said localized heating.3. A method as claimed in claim 2 further including producing as saidrepresentation, a representation of an instantaneous spatial temperaturedistribution in the workpiece.
 4. A method as claimed in claim 3 furtherincluding producing an instantaneous spatial temperature errordistribution as a function of the desired spatial temperaturedistribution and said instantaneous spatial temperature distribution. 5.A method as claimed in claim 4 further including absorbing radiationexitant from said surface.
 6. A method as claimed in claim 5 whereinproducing said representation includes producing at least one signalrepresentative of radiation intensity from said surface.
 7. A method asclaimed in claim 5 further including controlling the amount of saidlocalized heating by irradiating in response to said instantaneousspatial temperature error distribution.
 8. A method as claimed in claim7 wherein controlling the amount of said localized heating includescontrolling the exposure of each of said areas to radiation.
 9. A methodas claimed in claim 7 wherein controlling the amount of said localizedheating includes controlling the amount of radiation to which each ofsaid areas is exposed.
 10. A method as claimed in claim 2 whereinirradiating includes irradiating the workpiece with primary andcorrective energy sources.
 11. A method as claimed in claim 10 whereinirradiating further includes varying irradiance produced by at least oneof said primary and corrective energy sources.
 12. A method as claimedin claim 11 further including storing said representation.
 13. A methodas claimed in claim 5 wherein absorbing includes absorbing saidradiation exitant from said surface in a radiation absorbingenvironment.
 14. A method as claimed in claim 13 wherein absorbingincludes absorbing said radiation exitant from said surface in at leastone radiation absorbing surface.
 15. A method as claimed in claim 14further including cooling said at least one radiation absorbing surface.16. A method as claimed in claim 2 wherein exposing includes directingradiation from at least one energy source to said surface.
 17. A methodas claimed in claim 16 wherein exposing further includes selectivelyvarying as a function of said representation, a variable opacity of eachof a plurality of filter portions of a filtering member interposedbetween said at least one energy source and said surface.
 18. A methodas claimed in claim 2 wherein exposing includes directing radiation fromat least one energy source to a reflecting member.
 19. A method asclaimed in claim 18 wherein exposing further includes reflecting saidradiation from said reflecting member to said surface.
 20. A method asclaimed in claim 19 wherein exposing further includes selectivelyvarying, as a function of said representation, a variable reflectivityof each of a plurality of reflector portions of said reflecting member.21. A method as claimed in claim 2 wherein exposing includes reflectingradiation thermally emitted by said surface back to said surface.
 22. Amethod as claimed in claim 21 wherein exposing further includesselectively varying, as a function of said representation, a variablereflectivity of each of a plurality of reflector portions of areflecting member oriented to reflect radiation thermally emitted bysaid surface back to said surface.
 23. A method as claimed in claim 2wherein exposing includes projecting radiation from an array of energysources onto said surface.
 24. A method as claimed in claim 23 whereinexposing further includes selectively varying, as a function of saidrepresentation, an intensity of radiation emitted by each of said energysources.
 25. A method as claimed in claim 2 wherein exposing includesscanning a laser beam across said surface.
 26. A method as claimed inclaim 25 wherein exposing further includes selectively varying, as afunction of said representation, a time during which said laser beamremains incident upon said surface in the vicinity of each of said areasrespectively.
 27. A method as claimed in claim 25 wherein exposingfurther includes selectively varying, as a function of saidrepresentation, a power of said laser beam in the vicinity of each ofsaid areas respectively.